"Kaminsky catalysts" are well known as olefin polymerization catalysts. The Kaminsky catalysts exhibit extremely high polymerization activity, and by the use of them, polymers of narrow molecular weight distribution can be obtained.
Transition metal compounds known as employable for the Kaminsky catalysts are, for example, bis (cyclopentadienyl) zirconium dichloride (see Japanese Patent Laid-Open Publication No. 19309/1983) and ethylenebis (4,5,6,7-tetrahydroindenyl) zirconium dichloride (see Japanese Patent Laid-Open Publication No. 130314/1986). It is also known that the olefin polymerization activity and the properties of the resulting polyolefins greatly vary when different transition metal compounds are used in the polymerization.
Recently, an olefin polymerization catalyst comprising a titanium amide compound having a titanium-nitrogen bond and an aluminoxane has been proposed as a novel olefin polymerization catalyst in, for example, Japanese Patent Laid-Open Publication No. 245713/1996.
Further, an organometallic complex having a metal of Group 4 of the periodic table, which contains a bis (borylamido) ligand represented by (Mes.sub.2 BNCH.sub.2 CH.sub.2 NBMes.sub.2).sup.-2, is described in "Organometallics", 1996, 15, 562-569. It is also described that this complex slightly exhibits ethylene polymerization activity.
By the way, polyolefins generally have excellent mechanical properties, so that they are used in many fields such as fields of various molded products. With the diversification of requirements for the properties of the polyolefins, polyolefins of various properties have been desired in recent years. Moreover, increase of productivity has been also desired.
Under such circumstances as mentioned above, there has been desired development of an olefin polymerization catalyst and a process for olefin polymerization each of which exhibits excellent olefin polymerization activity and is capable of producing polyolefins of excellent properties.